1. Field of the Invention
The present invention is broadly concerned with improved iron-complexing or scavenging compositions in solid or liquid form which include Sn.sup.+2 ion preferably derived from stannous chloride, as well as phos-acid(s) and alkali metal hexametaphosphate. The compositions of the invention can be used as a downhole well treatment or with sodium chloride to form a regenerating medium for cation exchange resins used in water softening systems.
2. Description of the Prior Art
Water softening systems have long been used in households and by industry to replace hardness cations such as calcium and magnesium with sodium ions. This is accomplished by passing an incoming water supply through a bed of sodium charged cation exchange resin beads or particles. As the water passes through the cation exchange resin bed, the incident hardness cations are exchanged for the sodium ions of the bed. In the course of time, the ion exchange resin bed becomes saturated with hardness cations removed from the incoming water, and it is necessary to recharge the bed by passing a brine solution primarily consisting of sodium chloride through the resin bed. This replenishes the bed with sodium ions and removes unwanted calcium, magnesium, or other ions previously removed from the water.
Over time, the exchange capacity of an ion exchange resin bed deteriorates as impurities in the incoming water collect in the resin bed and are not removed by periodic recharging. At some point, depending primarily on the characteristics of the incoming water supply, the resin bed becomes unacceptably "fouled," i.e., the resin bed's capacity to soften water has been diminished to an extent that it must be specially treated to restore softening capacity.
Although a number of factors can lead to fouling of an ion exchange resin bed, perhaps the greatest single contributing factor is the presence of iron in an incoming water supply. Iron can exist in several valence states in water, the most common being the ferrous and ferric states. It is most desirable to maintain the iron in the ferrous state, inasmuch as ferrous iron can readily be removed during conventional resin bed regeneration. However, ferrous iron tends to become oxidized to the ferric state after being exchanged onto a resin bed, which makes its removal very difficult and can cause the resin beads to split.
Iron also presents significant problems in the context of oil well drilling operations. For example, excessive iron in oil well fluids can lead to the formation of viscous downhole emulsions which can block flow and significantly minimize oil production. Accordingly, oil well operators need to carefully monitor and to the extent possible inhibit the formation of viscous emulsions of this type.